Studies in laboratory animals suggest that prostaglandins mediate ongoing bone resorption and that estrogen inhibits prostaglandin synthesis. An investigation was begun to test the hypothesis that diclofenac sodium, a nonsteroidal anti-inflammatory drug, would be useful in preventing postmenopausal bone loss. Results in premenopausal women indicate that the drug produced a 20% decrease in urinary calcium and in postmenopausal women a 40% decrease in urinary calcium.